Large quantities of electronic components of wireless communication apparatus for transmission of large data volume are mounted in today's electronic devices such as cell phones and tablet terminals. A problem of such electronic components for wireless communications is that they not only tend to generate noise, but are highly sensitive to noise, which causes malfunctions when exposed to external noise.
On the other hand, there is a demand for increasing the mount density of electronic components to make smaller and lighter electronic devices with advanced functionality. A problem of increasing the mount density is that it increases not only the number of electronic components that generate noise, but the number of electronic components affected by the noise.
A known conventional approach to this problem is shield packaging, whereby the noise-generating electronic components are covered in packages with a shielding layer to prevent noise generation from the electronic components, and noise entry into the electronic components. For example, Patent Literature 1 describes that an electromagnetic shield member having a high shielding effect can be easily obtained by spraying (atomizing) a conductive or semi-conductive material onto package surfaces to coat the package. A problem, however, is that desirable shielding performance may not be obtained, and the adhesion between the shielding layer and the package is poor when the shielding layer is formed by spray coating with a solution of metallic particles in a solvent.
A efficient production of a shielded package, for example, as described in Patent Literature 2a circuit module producing method is known that includes the step of coating a plurality of ICs with an insulating layer, the step of coating the insulating layer with a shielding layer made of a conductive paste, and the step of dividing the substrate having formed the shielding layer thereon (a method that a cutting groove which is wider at the base end and narrower at the top end in the depth direction of the insulating layer is formed on the insulating layer before forming the shielding layer that covers the insulating layer, and the substrate is divided by being cut along the top end of the cutting groove with a width wider than the top end and narrower than the base end after forming the shielding layer by applying a conductive resin into the cutting groove). The shielding layer may be formed by using various methods, including transfer molding, potting, and vacuum printing, as described in this publication. However, these methods are problematic because they all require large equipment, and are likely to cause trapping of bubbles when filling grooves with a conductive resin.